Method and apparatus for transmitting and receiving client signal in optical transport network

ABSTRACT

Embodiments of the present invention provide a method and an apparatus for transmitting and receiving a client signal in an optical transport network. In the transmission method, a received client signal is mapped into a variable-rate container OTU-N, wherein a rate of the OTU-N is N times as high as a preset reference rate; and then, the variable-rate container OTU-N is split into N optical sub-channel transport units OTUsubs by column, where a rate of each OTUsub equals to the reference rate; next, the N optical sub-channel transport units OTUsubs are modulated onto one or more optical carriers; at last, the one or more optical carriers is transmitted through a fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/373,005, filed on Dec. 8, 2016, which is a continuation of U.S.patent application Ser. No. 14/609,232, filed on Jan. 29, 2015, now U.S.Pat. No. 9,531,477, which is a continuation of International ApplicationNo. PCT/CN2013/071898, filed on Feb. 26, 2013, which claims priority toChinese Patent Application No. 201210268385.0, filed on Jul. 30, 2012.All of the afore-mentioned patent applications are hereby incorporatedby reference in their entireties.

TECHNICAL FIELD

The present invention relates to the field of optical transportnetworks, and in particular, to a method and an apparatus fortransmitting and receiving a client signal in an optical transportnetwork.

BACKGROUND

As a core technology of a next-generation transport network, an OTN(Optical transport network) includes electric-layer and optical-layertechnical specifications, features diverse OAM (Operation,Administration and Maintenance), and is capable of powerful TCM (TandemConnection Monitoring) and outband FEC (Forward Error Correction),allowing flexible scheduling and management for large-capacity services.

On an electric processing layer, the OTN technology defines a standardencapsulation structure, which maps various client services, and canimplement management and monitoring for client signals. An OTN framestructure is shown in FIG. 1, the OTN frame is a structure of 4×4080bytes, that is, 4 rows×4080 columns. The OTN frame structure includes aframe delimiting area, OTUk (Optical Channel Transport Unit) OH(Overhead), ODUk (Optical Channel Data Unit) OH, OPUk (Optical ChannelPayload Unit) OH, an OPUk payload area (Payload Area), and a FEC area,where values 1, 2, 3, and 4 of k correspond to rate levels 2.5 G, 10 G,40 G, and 100 G respectively. The frame delimiting area includes an FAS(Frame Alignment Signal) and an MFAS (Multi-frame Alignment Signal),information in the OPUk OH is primarily used for mapping and adaptationmanagement of a client service, information in the ODUk OH is primarilyused for managing and monitoring an OTN frame, and information in theOTUk OH is primarily used for monitoring a transmission section. A fixedrate of the OTUk is called a line interface rate. Currently, lineinterface rates of four fixed rate levels 2.5 G, 10 G, 40 G, and 100 Gexist. The OTN transmits a client signal in the following manner:mapping an upper-layer client signal to an OPUj of a lower rate leveland adding OPUj overhead and ODUj overhead to form an ODUj, which isherein called a lower-order ODUj; and then mapping the lower-order ODUjto an OPUk of a higher rate level, and adding OPUk overhead, ODUkoverhead, OTUk overhead, and a FEC to form a constant-rate OTUk, wherethe OTUk is called a higher-order OTUk; and modulating the higher-orderOTUk onto a single optical carrier for transmission, where a bearerbandwidth of the optical carrier is equal to a fixed rate of thehigher-order OTUk. In addition, an ODUflex is introduced in an existingOTN, and is called a lower-order variable-rate optical channel dataunit, and is used to carry an upper-layer service of any rate. Thelower-order ODUflex needs to be mapped to the higher-order OPUk first,and the OPUk overhead, the ODUk overhead, the OTUk overhead, and the FECare added to form a constant-rate higher-order OTUk, and then thehigher-order OTUk is modulated onto a single optical carrier fortransmission.

Massive increase and flexible change of upper-layer client IP (InternetProtocol) services impose challenges to an optical transport networksystem. Currently, optical spectrum resources are divided according to50 GHz optical spectrum grid bandwidths, and a 50 GHz optical spectrumgrid bandwidth is allocated to each optical carrier. For opticalcarriers whose bearer bandwidths fall within the four fixed rate levels2.5 G, 10 G, 40 G, and 100 G, optical spectrum width occupied by theoptical carriers does not reach 50 GHz, and waste of optical spectrumresources exists. Moreover, the optical spectrum is a limited resource.To make full use of optical spectrum resources, improve overalltransmission capabilities of a network, and fulfill increasingupper-layer client IP (Internet Protocol, protocol for interconnectionbetween networks) service transmission, a Flex Grid (flexible grid)technology is introduced into an optical layer to extend the opticalspectrum grid bandwidth division of the optical spectrum resources froma constant 50 GHz granularity (ITU-T (International TelecommunicationUnion-Telecommunication Standardization Sector-telecommunication) G.694)to optical spectrum grid bandwidth division of a smaller granularity.Currently, a minimum optical spectrum grid bandwidth granularity isslot=12.5 GHz, and an optical carrier can occupy one or more continuousoptical spectrum grid bandwidths. The OTN network may allocate a properoptical spectrum width according to a traffic volume of a client signalto be transmitted and a transmission distance, so as to meettransmission requirements.

In addition, persons in the art expect to increase spectrum efficiencyas far as possible. To obtain higher spectrum efficiency, higher-ordermodulation is required, such as nQAM (n-order quadrature amplitudemodulation) and an orthogonal frequency division multiplexing (OFDM,Orthogonal Frequency Division Multiplexing) technologies. That is, undera constant spectrum width, actual traffic volume requirements arefulfilled by changing an optical carrier modulation format.

However, currently an electric-layer OTN line interface has a fixed ratelevel, and it is not practicable to provide a line interface of a properrate according to the actual traffic volume of the client service, andtherefore, optimal configuration of optical transport network bandwidthresources is not available.

SUMMARY

Embodiments of the present invention provide a method and an apparatusfor transmitting and receiving a client signal in an optical transportnetwork.

According to one aspect, an embodiment of the present invention providesa method for transmitting a client signal in an optical transportnetwork, where the method includes: mapping a received client signalinto a variable-rate container OTU-N, where a rate of the OTU-N is Ntimes of a preset reference rate level, and the value N is a positiveinteger that is configurable as required; splitting the variable-ratecontainer OTU-N into N optical sub-channel transport units OTUsubs bycolumn, where a rate of each OTUsub is equal to the reference ratelevel; modulating the N optical sub-channel transport units OTUsubs ontoone or more optical carriers; and sending the one or more opticalcarriers onto a same fiber for transmission.

According to another aspect, an embodiment of the present inventionprovides a transmission apparatus in an optical transport network, wherethe transmission apparatus includes a constructing module, a mappingmodule, a splitting module, a modulating module, and a transmittingmodule. The constructing module is configured to construct avariable-rate container OTU-N, where a rate of the OTU-N is N times ashigh as a preset reference rate level, and the value N is a positiveinteger that is configurable as required; the mapping module isconfigured to map a received client signal into the OTU-N; the splittingmodule is configured to split the OTU-N, in which the client signal ismapped, into N optical sub-channel transport units OTUsubs by columns,where a rate of each OTUsub is the reference rate level; the modulatingmodule is configured to modulate the N OTUsubs onto one or more opticalcarriers; and the transmitting module is configured to send the one ormore optical carriers onto a same fiber for transmission.

According to another aspect, an embodiment of the present inventionprovides a method for receiving a client signal in an optical transportnetwork, where the method includes: receiving one or more opticalcarriers from a same fiber; demodulating the N optical sub-channeltransport units OTUsubs out of the one or more optical carriers;aligning the N OTUsubs, where a rate of each OTUsub is a presetreference rate level; multiplexing the aligned N OTUsubs into onevariable-rate container OTU-N by interleaving columns, where a rate ofthe OTU-N is N times as high as the reference rate level, and the valueN is a positive integer that is configurable as required; and demappinga client signal from the OTU-N.

According to another aspect, an embodiment of the present inventionprovides a receiving apparatus in an optical transport network, wherethe receiving apparatus includes a receiving interface, a demodulatingmodule, an aligning module, a multiplexing module, and a demappingmodule. The receiving interface is configured to receive one or moreoptical carriers from a same fiber. The demodulating module isconfigured to demodulate the N optical sub-channel transport unitsOTUsubs out of the one or more optical carriers received by thereceiving interface. The aligning module is configured to align the NOTUsubs demodulated by the demodulating module. The multiplexing moduleis configured to multiplex the N OTUsubs, which are aligned by thealigning module, into one variable-rate container OTU-N by interleavingcolumns, where a rate of the OTU-N is N times as high as the referencerate level, and the value N is a positive integer that is configurableas required. The demapping module is configured to demap a client signalfrom the OTU-N generated by the multiplexing module.

According to another aspect, an embodiment of the present inventionprovides a transmission apparatus in an optical transport network, wherethe apparatus includes at least one processor. The at least oneprocessor is configured to: map a received client signal into avariable-rate container OTU-N, where a rate of the OTU-N is N times ashigh as a preset reference rate level, and the value N is a positiveinteger that is configurable as required; split the variable-ratecontainer OTU-N into N optical sub-channel transport units OTUsubs bycolumn, where a rate of each OTUsub is equal to the reference ratelevel; modulate the N optical sub-channel transport units OTUsubs ontoone or more optical carriers; and send the one or more optical carriersonto a same fiber for transmission.

According to another aspect, an embodiment of the present inventionprovides a receiving apparatus in an optical transport network, wherethe apparatus includes a demodulator and at least one processor. Thedemodulator is configured to demodulate N optical sub-channel transportunits OTUsubs out of received optical carriers. The at least oneprocessor is configured to: receive one or more optical carriers from asame fiber; demodulate the N optical sub-channel transport units OTUsubsout of the one or more optical carriers; align the N OTUsubs, where arate of each OTUsub is a preset reference rate level; multiplex thealigned N OTUsubs into one variable-rate container OTU-N by interleavingcolumns, where a rate of the OTU-N is N times as high as the referencerate level, and the value N is a positive integer that is configurableas required; and demap a client signal from the OTU-N.

In the embodiments, a client signal is mapped into a variable-ratecontainer OTU-N and the OTU-N is transmitted by using the same fiber, soas to be adaptable to change of optical-layer spectrum bandwidths andaccomplish optimal configuration of optical transport network bandwidthresources.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly introduces theaccompanying drawings required for describing the embodiments.Apparently, the accompanying drawings in the following description showmerely some embodiments of the present invention, and a person ofordinary skill in the art may still derive other drawings from theseaccompanying drawings without creative efforts.

FIG. 1 is a structural diagram of an OTN frame provided in the priorart;

FIG. 2 is a schematic diagram of a frame structure of a variable-ratecontainer OTU-N generated out of an OTN frame by interleaving columnsaccording to an embodiment of the present invention;

FIG. 3 to FIG. 5 are schematic structural diagrams of a variable-ratecontainer OTU-N according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of dividing an optical channel payloadunit OPU-N of a variable-rate container OTU-N into tributary slotsaccording to an embodiment of the present invention;

FIG. 7 is a flowchart of a method for transmitting a client signal in anOTN according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of mapping two lower-order ODUts into avariable-rate container OTU-N according to an embodiment of the presentinvention;

FIG. 9 is a schematic diagram of splitting a variable-rate containerOTU-N into a plurality of optical sub-channel transport units OTUsubs bycolumns according to an embodiment of the present invention;

FIG. 10 is a schematic diagram of splitting a frame header of avariable-rate container OTU-3 by columns according to an embodiment ofthe present invention;

FIG. 11 is a flowchart of a method for receiving a client signal in anoptical transport network according to an embodiment of the presentinvention;

FIG. 12 is a schematic diagram of a transmission apparatus in an opticaltransport network according to an embodiment of the present invention;

FIG. 13 is a schematic diagram of a receiving apparatus in an opticaltransport network according to an embodiment of the present invention;

FIG. 14 is a schematic diagram of another receiving apparatus in anoptical transport network according to an embodiment of the presentinvention;

FIG. 15 is a block diagram of a transmission apparatus in an opticaltransport network according to an embodiment of the present invention;and

FIG. 16 is a block diagram of a receiving apparatus in an opticaltransport network according to an embodiment of the present invention.

DETAILED DESCRIPTION

To make the objectives, technical solutions, and advantages of thepresent invention clearer, the following further describes theimplementation manners of the present invention in detail with referenceto the accompanying drawings.

The embodiments of the present invention construct a variable-ratecontainer structure called OTU-N(Optical channel Transport Unit-N) on anOTN electric layer, where the value N is a configurable positiveinteger, and a rate of the OTU-N is configurable using a presetreference rate level as a granularity. For example, the rate of theOTU-N is N times as high as the reference rate level. The rate of theOTU-N may be configured flexibly according to a traffic volume of aclient signal. The traffic volume of the client signal may be detectedby an OTN device, or configured by a management plane.

The value N is configured flexibly according to transmissionrequirements. Preferably, the value N is determined based on the trafficvolume of the client signal and the reference rate level. For example,the value N is equal to a round-up result of dividing the traffic volumeof the client signal by the reference rate level. Rounding up a quotientof dividing A by B means that if A is divisible by B, a round-upquotient of dividing A by B is equal to a quotient of dividing A by B;and, if A is not divisible by B, a round-up quotient of dividing A by Bis equal to a value of adding 1 to a value obtained by rounding thequotient of dividing A by B. For example, if the traffic volume of theclient signal is 200 G and the reference rate level is set to 25 G, thevalue N is a quotient 8 of dividing 200 G by 25 G, that is, N=8; and, ifthe traffic volume of the client signal is 180 G and the reference ratelevel is set to 25 G, the value N is equal to adding 1 to a value 7obtained by rounding a quotient 7.2 of dividing 180 G by 25 G, that is,N=8.

The preset fixed value of the reference rate level includes but is notlimited to the following types:

1. The reference rate level may be a rate of an OTU1, an OTU2, an OTU3,or an OTU4 defined in the ITU-T G.709 standard, that is, the referencerate level is selected among 2.5 G, 10 G, 40 G, and 100 G, and ispreferably 100 G, that is, the rate of the OTU4.

2. The reference rate level may be an integral multiple of an opticalspectrum grid bandwidth defined in the ITU-T G.694. For example, if theoptical spectrum grid bandwidth is 12.5 GHz, the reference rate level isselected among 12.5 G, 25 G, 50 G, and 100 G, and is preferably 25 G.

The client signal includes:

(1) client data, a CBR (Constant Bit Rate) service, and a Packet(packet) service, and

(2) lower-order ODUt services, including an ODU0, an ODU1, an ODU2, anODU2 e, an ODU3, an ODU4, and an ODUflex that are defined in the ITU-TG.709 standard.

A frame structure of the OTU-N varies with the value N, and is formed ofN subframes by interleaving columns, and a rate of each subframe is thereference rate level. If the subframe has M columns, which include M1columns of overhead, M2 columns of payload, and M3 columns of FEC, thenthe OTU-N has M*N columns, including M I*N columns of overhead, M2*Ncolumns of payload, and M3*N columns of FEC.

Preferably, as shown in FIG. 2 to FIG. 5, the frame structure of theOTU-N is formed of N portions of OTN frames by interleaving columns, andincludes 4 rows and 4080*N columns, where a 1^(st) column to a 14N^(th)column include an OTU-N frame delimiting area, an OTU-N overhead area,and an ODU-N overhead area; the (14N+1)^(th) column to the 16N^(th)column are an OPU-N overhead area, the (16N+1)^(th) column to the3824N^(th) column are an OPU-N payload area, and the (3824N+1)^(th)column to the 4080N^(th) column are a FEC (forward error correction)overhead area.

Preferably, as shown in FIG. 3, all overhead information of one of theOTN frames serves as overhead information of the OTU-N, and, forremaining (N−1) OTN frames, only their FAS (Frame Alignment Signal) andMFAS (Multi-frame Alignment Signal) are placed in an overhead area ofthe first row and the 1^(st) to 7N^(th) columns of the OTU-N.

An optical channel data unit corresponding to the OTU-N is called anODU-N, and an optical channel payload unit corresponding to the OTU-N iscalled an OPU-N. The following two schemes are available for dividingthe OPU-N into TSs (Tributary Slot):

Scheme 1: As shown in FIG. 6, the OPU-N is divided into N tributaryslots by column, a rate of each tributary slot is the reference ratelevel, and the value N mentioned throughout this document has the samevalue, where the (14N+1)^(th) column to the 16N^(th) are a tributaryslot overhead area (TSOH), and the (16N+1)^(th) column to the 3824N^(h)column are an OPU-N payload area.

Scheme 2: Similar to a manner described in the ITU-T G.709 standard,which divides an OTU4 into 80 tributary slots of 1.25 G, the OTU-N isdivided into tributary slots by bytes and using a 1.25 G rate level as agranularity. For example, an OTU4-4 of a 400 G rate level (the OTU4-4 isthe OTU-N that is formed of four OTU4 s by interleaving columns) may bedivided into 320 tributary slots of 1.25 G. In the ITU-T G.709 standard,a manner of dividing the OTU4 is to divide an OPU4 payload area into 80tributary slots of 1.25 G by interleaving bytes at intervals of 80multiframes. In the embodiment of the present invention, the manner ofdividing the OTU4-4 may be to divide the OPU4-4 payload area into 320tributary slots of 1.25 G by interleaving bytes at intervals of 80multiframes.

Referring to FIG. 7, an embodiment provides a method for transmitting aclient signal in an optical transport network. The method includes thefollowing steps:

Step 101: Map a received client signal into an OTU-N.

For client data, the client data is mapped into a tributary slot of anOPU-N by using a GMP (Generic Mapping Procedure) or GFP (Generic FramingProcedure) mapping manner, and then OPU-N overhead is added, ODU-Noverhead is added into the OPU-N to form an ODU-N, and OTU-N overheadand FEC (Forward Error Correction) information are added into the ODU-Nto form an OTU-N.

For a lower-order ODUt service, one lower-order ODUt service is mappedto an ODTU-N.ts (Optical channel Data Tributary Unit-N) of the OPU-N byusing a GMP manner, where ts is the number of OPU-N tributary slotsoccupied by the lower-order ODUt; the ODTU-N.ts is multiplexed into tstributary slots of the OPU-N; ODU-N overhead is added into the OPU-N toform an ODU-N; and OTU-N overhead and FEC are added into the ODU-N toform an OTU-N.

Preferably, a granularity of bytes used for mapping each lower-orderODUt is the same as the number of OPU-N tributary slots occupied by thelower-order ODUt. To make it easier for persons skilled in the art tounderstand the mapping method in this embodiment, the following gives anexample with reference to FIG. 8. It is assumed that an OTU-3 carriestwo lower-order ODUts, where the two lower-order ODUts are a firstlower-order ODUt and a second lower-order ODUt. The first lower-orderODUt occupies one tributary slot of the OPU-3, such as TS1; and thesecond lower-order ODUt occupies two tributary slots of the OPU-3, suchas TS2 and TS3. An optical channel data tributary unit of the OPU-3 iscalled an ODTU-3.ts, where the ODTU-3.ts includes TSOH (tributary slotoverhead) and TS payload, and ts is the number of OPU-3 tributary slotsoccupied by the ODTU-3.ts.

As shown in FIG. 8, a specific process in which the two lower-orderODUts are mapped and multiplexed to the OTU-3 is as follows:

(1) The first lower-order ODUt is mapped into the ODTU-3.1 at agranularity of 1 byte according to the GMP, where the ODTU-3.1 occupiesone tributary slot TS1 of the OPU-3; and mapping information is addedinto tributary slot overhead TSOH1 corresponding to the tributary slotTS1.

(2) The second lower-order ODUt is mapped into the ODTU-3.2 at agranularity of 2 bytes through GMP, where the ODTU-3.2 occupies twotributary slots TS1 and TS2 of the OPU-3; and mapping information isadded into a TSOH corresponding to either of the two tributary slots,for example, added into tributary slot overhead TSOH2 corresponding tothe tributary slot TS2.

(3) The ODTU-3.1 and the ODTU-3.2 are multiplexed into one OPU-3, ODU-3overhead is added into the OPU-3 to generate an ODU-3, and OTU-Noverhead is added into the ODU-3 to generate the OTU-3. In thisembodiment, a plurality of ODTU-N.tss is multiplexed into one OPU-N toreduce overhead management complexity.

This embodiment inherits a definition manner of PT (Payload Type) in theITU-T G.709 standard. It is noteworthy that a new PT such as PT=0x22 maybe added in this embodiment to indicate that the ODU-N carries aplurality of lower-order services in a hybrid manner.

This embodiment may also inherit a definition manner of an MSI(Multiplex Structure Identifier) in the ITU-T G.709 standard. After theODU-N mapped to a plurality of ODUts is obtained, the MSI of the ODU-Nis modified to indicate whether each tributary slot in the ODU-N isalready occupied by the lower-order ODUt service. Certainly, thedefinition of the PT and the MSI is not limited to the foregoingmanners, and is not specifically limited in this embodiment.

Step 102: As shown in FIG. 9, the OTU-N is split into N OTUsubs (Opticalsub-channel Transport Unit) by columns, where a rate of each OTUsub isthe reference rate level.

The following two schemes are available for splitting the OTU-N into NOTUsubs by columns:

Scheme 1: Split the OTU-N into N sub-channels by columns, and performFEC for each sub-channel and add FEC overhead information to obtain theN OTUsubs. Preferably, one of the sub-channels includes OTU-N overhead,ODU-N overhead, an FAS, and an MFAS, and other N−1 sub-channels includethe FAS and the MFAS, where a rate of each sub-channel is equal to thereference rate level. FEC is performed on each sub-channel, which canreduce difficulty of FEC.

Scheme 2: Perform FEC for the OTU-N and add the FEC overhead informationto obtain processed OTU-N, and split the processed OTU-N into the NOTUsubs by columns. Preferably, one of the OTUsubs includes the OTU-Noverhead, the ODU-N overhead, the FAS, and the MFAS, and other N−1OTUsubs include the FAS and the MFAS, where the rate of each OTUsub isequal to the reference rate level.

In this embodiment, to facilitate identification of each OTUsub, theOTUsub may also carry an LLM (Logical Lane Marker). The logical lanemarker occupies a 6^(th) byte of the FAS, and is denoted by LLMi, wherethe LLMi is a lane marker of each OTUsub, and its value range may be 0to 255. The LLMi 0 to 255 mark the 0^(th) to 255^(th) OTUsubsrespectively. If the number of OTUsubs is greater than 256, an extendeddefinition may be performed in a reserved area of in other overhead.Using three OTUsubs as an example, a frame header of the OTUsub is shownin FIG. 10, the values of the logical lane markers LLM1, LLM2, and LLM3carried in the 0^(th) to 2^(th) OTUsubs are 0, 1, and 2 respectively,and occupy the 6^(th) byte of frame header overhead, where OA1 and OA2represent other overhead of the OTUsub frame header, which is notspecifically limited in this embodiment. The 7^(th) byte is an MFASbyte, which is not repeated in this embodiment.

Step 103: Modulate the N OTUsubs onto one or more optical carriers.

(1) For a single carrier, the N OTUsubs are modulated onto a singleoptical carrier.

For example, assuming that a traffic volume of the client signal is 400G and that the reference rate level of the OTU-N is set to 100 G, thevalue N is equal to 4, and a bearer bandwidth of the single carrier isset to 400 G.

The number of optical spectrum grid bandwidths occupied by the singlecarrier and an applied modulation format (a modulation order is k) arenot limited. For example, if the single carrier occupies four 12.5 Goptical spectrum grid bandwidths, then a PM-16QAM (PolarizationMultiplexing-16^(th)-order quadrature amplitude modulation) modulationformat (the modulation order is 16) is used. Calculated by using aformula 2*4*12.5 Gbit/s*log₂ 16, the bandwidth of the single carrier maybe up to 400 G bandwidth, which meets a requirement of transmitting theclient signal.

If the single carrier occupies eight 12.5 G optical spectrum gridbandwidths, then a 16QAM (16^(th)-order quadrature amplitude modulation)modulation format (the modulation order is 16) is used. Calculated byusing a formula 8*12.5 Gbit/s*log₂ 16, the bandwidth of the singlecarrier may also be up to 400 G, which meets the requirement oftransmitting the client signal.

(2) For a plurality of optical subcarriers, when the N OTUsubs aremodulated onto M subcarriers, the N OTUsubs are divided into M groups,where the value M is a positive integer, and each group of OTUsubs ismodulated onto a subcarrier. The value N is configured as an integralmultiple of the value M. For example, the value M may be set to arounded-up quotient of dividing the traffic volume of the client signalby the bearer bandwidth of one subcarrier. Preferably, N is equal to M.Preferably, the M subcarriers may employ an orthogonal frequencydivision multiplexing manner.

For example, assuming that the traffic volume of the client signal is400 G and that the reference rate level of the OTU-N is set to 25 G, thevalue N is equal to 16. That is, the OTU-16 is split into 16 OTUsubs,and the bearer bandwidth of the M subcarriers is set to 400 G to meetthe requirement of transmitting the client signal.

If the bearer bandwidth of each subcarrier is 50 G, the value M is setto 8. That is, 16 OTUsubs are modulated onto 8 subcarriers fortransmission. In this case, every 2 OTUsubs are modulated onto onesubcarrier.

The number (m) of optical spectrum grid bandwidths occupied by eachsubcarrier and the used modulation format (the modulation order is k)are not limited. For example, if each subcarrier occupies four 12.5 Goptical spectrum grid bandwidths, then a BPSK (Binary Phase ShiftKeying) modulation format (the modulation order is 2) is used.Calculated by using a formula 4*12.5 Gbit/s*log₂ 2, the bandwidth ofeach subcarrier may be up to 50 G.

If each subcarrier occupies one 12.5 G optical spectrum grid bandwidth,then a PM-QPSK (Polarization Multiplexing-polarization multiplexingquadrature phase shift keying) modulation format (the modulation orderis 4) is used. Calculated by using a formula 2*12.5 Gbit/s*log₂ 4, thebandwidth of each subcarrier may also be up to 50 G.

Step 104: Send the one or more optical carriers onto a same fiber fortransmission.

In this embodiment, a client signal is mapped into a variable-ratecontainer OTU-N and the OTU-N is transmitted by using a same fiber, soas to be adaptable to change of optical-layer spectrum bandwidths andaccomplish optimal configuration of optical transport network bandwidthresources.

Referring to FIG. 11, corresponding to the foregoing method fortransmitting a client signal in an OTN, an embodiment provides a methodfor receiving a client signal in an optical transport network,including:

Step 501: Receive one or more optical carriers from a same fiber.

Step 502: Demodulate the N OTUsubs (optical sub-channel transport unit)out of the one or more optical carriers.

Step 503: Align the N OTUsubs, where a rate of each OTUsub is a presetreference rate level.

The aligning the N OTUsubs includes: performing frame delimiting for theN OTUsubs according to an FAS (Frame Alignment Signal) of each OTUsub,and aligning frame headers of the N OTUsubs that have undergone theframe delimiting.

In this embodiment, optionally, in the aligning, the N OTUsubs may bealigned based on frame headers, and the N OTUsubs may be further alignedby using the MFAS carried in each OTUsub. That is, after the N OTUsubsare aligned, not only the frame headers keep aligned, but also the MFAS(Multiframe Alignment Signal) carried in each OTUsub needs to keepconsistent. An alignment manner applied in a specific implementationprocess is not specifically limited in this embodiment.

Step 504: Multiplex the aligned N OTUsubs into one OTU-N by interleavingcolumns, where a rate of the OTU-N is N times as high as the referencerate level, and the value N is a positive integer that is configurableas required.

Optionally, the following two schemes are available for multiplexing thealigned N OTUsubs into one OTU-N by interleaving columns:

Scheme 1: Perform FEC decoding for the aligned N OTUsubs, and thenmultiplex the N OTUsubs, which have undergone the FEC decoding, into oneOTU-N by interleaving columns.

Scheme 2: Multiplex the aligned N OTUsubs into one OTU-N by interleavingcolumns, and perform the FEC decoding for the OTU-N.

Step 505: Demap a client signal from the OTU-N.

The demapping a client signal from the OTU-N includes: parsing OPU-N(optical channel payload unit) overhead of the OTU-N to obtain mappinginformation carried in tributary slot overhead corresponding to eachtributary slot in the OTU-N; and demapping the client signal from eachtributary slot payload area of the OTU-N based on the mappinginformation.

Referring to FIG. 12, an embodiment provides a transmission apparatus inan optical transport network. The transmission apparatus 60 includes aconstructing module 601, a mapping module 603, a splitting module 605, amodulating module 607, and a transmitting module 609.

The constructing module 601 is configured to construct a variable-ratecontainer structure that is called an OTU-N, where a rate of the OTU-Nis N times as high as a preset reference rate level, the value N is aconfigurable positive integer, the value N is flexibly configurabledepending on transmission requirements, and preferably, the value N isdetermined based on a traffic volume of the client signal and thereference rate level.

The mapping module 603 is configured to map a received client signalinto the OTU-N constructed by the constructing module 601.

For client data, the client data is mapped by the mapping module 603into a tributary slot of an OPU-N by using a GMP (Generic MappingProcedure) or GFP (Generic Framing Procedure) mapping manner, and thenOPU-N overhead is added, ODU-N overhead is added into the OPU-N to forman ODU-N, and OTU-N overhead and FEC (Forward Error Correction)information are added into the ODU-N to form an OTU-N.

For a lower-order ODUt service, one lower-order ODUt service is mappedby the mapping module 603 to an ODTU-N.ts (Optical channel DataTributary Unit-N) of the OPU-N by using a GMP mapping manner, where tsis the number of OPU-N tributary slots occupied by the lower-order ODUt;the ODTU-N.ts is multiplexed into ts tributary slots of the OPU-N; ODU-Noverhead is added into the OPU-N to form an ODU-N; and OTU-N overheadand FEC are added into the ODU-N to form an OTU-N. Preferably, agranularity of bytes used by the mapping module 603 for mapping eachlower-order ODUt is the same as the number of OPU-N tributary slotsoccupied by the lower-order ODUt.

As shown in FIG. 9, the splitting module 605 is configured to split theOTU-N, in which the client signal is mapped by the mapping module 603,into N OTUsubs (Optical sub-channel Transport Unit) by columns, where arate of each OTUsub is the reference rate level.

The following two schemes are available for the splitting module 605 tosplit the OTU-N into N OTUsubs by columns:

Scheme 1: Split the OTU-N into N sub-channels by columns, and performFEC for each sub-channel and add FEC overhead information to obtain theN OTUsubs. Preferably, one of the sub-channels includes OTU-N overhead,ODU-N overhead, an FAS, and an MFAS, and other N−1 sub-channels includethe FAS and the MFAS, where the rate of each sub-channel is equal to thereference rate level. FEC is performed on each sub-channel, which canreduce difficulty of FEC.

Scheme 2: Perform FEC for the OTU-N and add the FEC overhead informationto obtain processed OTU-N, and split the processed OTU-N into the NOTUsubs by columns. Preferably, one of the OTUsubs includes the OTU-Noverhead, the ODU-N overhead, the FAS, and the MFAS, and other N−1OTUsubs include the FAS and the MFAS, where the rate of each OTUsub isequal to the reference rate level.

The modulating module 607 is configured to modulate the N OTUsubs, whichis a result of splitting by the splitting module 605, onto one or moreoptical carriers.

(1) For a single carrier, the modulating module 607 modulates the NOTUsubs onto a single optical carrier.

(2) For a plurality of optical subcarriers, for example, when themodulating module 607 modulates the N OTUsubs to M subcarriers, the NOTUsubs are divided into M groups, where the value M is a positiveinteger; and each group of OTUsubs is modulated onto a subcarrier. Thevalue N is set to an integral multiple of the value M. Preferably, N isequal to M. Preferably, the M subcarriers may employ an orthogonalfrequency division multiplexing manner.

The transmitting module 609 is configured to send the one or moreoptical carriers, which are modulated by the modulating module 607, ontoa same fiber for transmission.

It is noteworthy that each module included in the embodiments of thetransmission and receiving apparatuses is merely sorted according tofunctional logics but is not limited to the sorting so long as thecorresponding functions can be implemented. In addition, a specific nameof each functional module is merely intended for differentiating oneanother rather than limiting the protection scope of the presentinvention.

Referring to FIG. 13, an embodiment provides a receiving apparatus in anoptical transport network. The receiving apparatus 70 includes areceiving interface 701, a demodulating module 703, an aligning module705, a multiplexing module 707, and a demapping module 709.

The receiving interface 701 is configured to receive one or more opticalcarriers from a same fiber.

The demodulating module 703 is configured to demodulate the N OTUsubs(optical sub-channel transport unit) out of the one or more opticalcarriers received by the receiving interface 701.

The aligning module 705 is configured to align the N OTUsubs demodulatedby the demodulating module 703.

As shown in FIG. 14, the aligning module 705 includes a frame delimitingunit 705 a and an aligning unit 705 b. The frame delimiting unit 705 ais configured to perform frame delimiting for the N OTUsubs according toa frame alignment signal (FAS) of each OTUsub, and the aligning module705 b is configured to align frame headers of the N OTUsubs that haveundergone the frame delimiting.

The multiplexing module 707 is configured to multiplex the N OTUsubs,which are aligned by the aligning module 705, into one variable-ratecontainer OTU-N by interleaving columns, where a rate of the OTU-N is Ntimes as high as the reference rate level, and the value N is a positiveinteger that is configurable as required.

Referring to FIG. 14, the multiplexing module 707 includes a decodingunit 707 a and a multiplexing unit 707 b. Optionally, the decoding unit707 a is configured to perform FEC decoding for the aligned N OTUsubs;and the multiplexing unit 707 b is configured to multiplex the NOTUsubs, which have undergone the FEC decoding, into one OTU-N byinterleaving columns.

In another embodiment, the multiplexing unit 707 b is configured tomultiplex the aligned N OTUsubs into one OTU-N by interleaving columns;and the decoding unit 707 a is configured to perform the FEC decodingfor the OTU-N.

The demapping module 709 is configured to demap a client signal from theOTU-N generated by the multiplexing module 707.

Referring to FIG. 14, the demapping module 709 includes a parsing unit709 a and a demapping unit 709 b. The parsing module 709 a is configuredto parse OPU-N (optical channel payload unit) overhead of the OTU-N toobtain mapping information carried in tributary slot overheadcorresponding to each tributary slot in the OTU-N; and the demappingunit 709 b is configured to demap the client signal from each tributaryslot payload area of the OTU-N based on the mapping information.

The transmission and receiving apparatuses provided in the embodimentsmay be based on a same conception as the embodiment of methods fortransmitting and receiving a client signal respectively. For theirspecific implementation process, refer to the method embodiments, and nofurther details is provided herein.

It is noteworthy that each module included in the embodiments of thetransmission and receiving apparatuses is merely sorted according tofunctional logics but is not limited to the sorting so long as thecorresponding functions can be implemented. In addition, a specific nameof each functional module is merely intended for differentiating oneanother rather than limiting the protection scope of the presentinvention.

Refer to FIG. 15, which is a block diagram of an embodiment of atransmission apparatus in an optical transport network. The transmissionapparatus 90 includes at least one processor 904, where the at least oneprocessor 904 may be connected to a memory 902, and the memory 902 isconfigured to buffer a received client signal.

The at least one processor 904 is configured to perform the followingoperations: constructing a variable-rate container structure that iscalled an OTU-N, where a rate of the OTU-N is N times as high as apreset reference rate level, and the value N is a configurable positiveinteger; mapping the received client signal into an OTU-N; splitting theOTU-N into N OTUsubs (Optical sub-channel Transport Unit) by columns,where a rate of each OTUsub is the reference rate level; modulating theN OTUsubs onto one or more optical carriers; and sending the one or moreoptical carriers onto a same fiber for transmission.

The value N is flexibly configurable depending on transmissionrequirements, and preferably, the value N is determined based on atraffic volume of the client signal and the reference rate level.

For client data, the client data is mapped by the at least one processor904 into a tributary slot of an OPU-N by using a GMP (Generic MappingProcedure) or GFP (Generic Framing Procedure) mapping manner, and thenOPU-N overhead is added, ODU-N overhead is added into the OPU-N to forman ODU-N, and OTU-N overhead and FEC (Forward Error Correction)information are added into the ODU-N to form an OTU-N.

For lower-order ODUt services, one lower-order ODUt service is mapped bythe at least one processor 904 to an ODTU-N.ts (Optical channel DataTributary Unit-N) of the OPU-N by using a GMP manner, where ts is thenumber of OPU-N tributary slots occupied by the lower-order ODUt; theODTU-N.ts is multiplexed into ts tributary slots of the OPU-N; ODU-Noverhead is added into the OPU-N to form an ODU-N; and OTU-N overheadand FEC are added into the ODU-N to form an OTU-N. Preferably, agranularity of bytes used by the at least one processor 904 for mappingeach lower-order ODUt is the same as the number of OPU-N tributary slotsoccupied by the lower-order ODUt.

The following two schemes are available for the at least one processor904 to split the OTU-N into N OTUsubs by columns:

Scheme 1: Split the OTU-N into N sub-channels by columns, and performFEC for each sub-channel and add FEC overhead information to obtain theN OTUsubs. Preferably, one of the sub-channels includes OTU-N overhead,ODU-N overhead, an FAS, and an MFAS, and other N−1 sub-channels includethe FAS and the MFAS, where the rate of each sub-channel is equal to thereference rate level. FEC is performed on each sub-channel, which canreduce difficulty of FEC.

Scheme 2: Perform FEC for the OTU-N and add the FEC overhead informationto obtain processed OTU-N, and split the processed OTU-N into the NOTUsubs by columns. Preferably, one of the OTUsubs includes the OTU-Noverhead, the ODU-N overhead, the FAS, and the MFAS, and other N−1OTUsubs include the FAS and the MFAS, where the rate of each OTUsub isequal to the reference rate level.

For a single carrier, the at least one processor 904 modulates the NOTUsubs onto a single optical carrier.

For a plurality of optical subcarriers, for example, when the at leastone processor 904 modulates the N OTUsubs to M subcarriers, the NOTUsubs are divided into M groups, where the value M is a positiveinteger, and each group of OTUsubs is modulated onto a subcarrier. Thevalue N is set to an integral multiple of the value M. Preferably, N isequal to M. Preferably, the M subcarriers may employ an orthogonalfrequency division multiplexing manner.

Refer to FIG. 16, which is a block diagram of an embodiment of areceiving apparatus in an optical transport network. The receivingapparatus 110 includes a demodulator 1101 and at least one processor1104, where the at least one processor 1104 may be connected to a memory1102. The demodulator 1101 demodulates N OTUsubs (optical sub-channeltransport unit) out of received optical carriers, where the value N is apositive integer that is configurable as required. The memory 1102 isconfigured to buffer the N OTUs demodulated by the demodulator 1101.

The at least one processor 1104 is configured to perform the followingoperations: receiving one or more optical carriers from a same fiber;demodulating the N OTUsubs (optical sub-channel transport unit) out ofthe one or more optical carriers; aligning the N OTUsubs; multiplexingthe aligned N OTUsubs into one variable-rate container OTU-N byinterleaving columns, where a rate of the OTU-N is N times as high as apreset reference rate level, and the value N is a positive integer thatis configurable as required; and demapping a client signal from theOTU-N.

The aligning, by the at least one processor 1104, the N OTUsubs,includes: performing frame delimiting for the N OTUsubs according to aframe alignment signal (FAS) of each OTUsub, and aligning frame headersof the N OTUsubs that have undergone the frame delimiting.

The following two schemes are available for the at least one processor1104 to multiplex the aligned N OTUsubs into one OTU-N by interleavingcolumns:

Scheme 1: Perform FEC decoding for the aligned N OTUsubs, and thenmultiplex the N OTUsubs, which have undergone the FEC decoding, into oneOTU-N by interleaving columns.

Scheme 2: Multiplex the aligned N OTUsubs into one OTU-N by interleavingcolumns, and perform the FEC decoding for the OTU-N.

The demapping, by the at least one processor 1104, a client signal fromthe OTU-N, includes: parsing OPU-N (optical channel payload unit)overhead of the OTU-N to obtain mapping information carried in tributaryslot overhead corresponding to each tributary slot in the OTU-N; anddemapping the client signal from each tributary slot payload area of theOTU-N based on the mapping information.

A person of ordinary skill in the art may understand that all or a partof the steps of the embodiments may be implemented by hardware or aprogram instructing relevant hardware. The program may be stored in acomputer readable storage medium. The storage medium may include: aread-only memory, a magnetic disk, or an optical disc.

The foregoing descriptions are merely exemplary embodiments of thepresent invention, but are not intended to limit the present invention.Any modification, equivalent replacement, or improvement made withoutdeparting from the spirit and principle of the present invention shouldfall within the protection scope of the present invention.

What is claimed is:
 1. A method for transmitting a client signal in an optical transport network, the method comprising: mapping the client signal into an payload area of an optical channel transport unit-N (OTU-N), wherein a rate of the OTU-N is N times a reference rate, and the value N is a positive integer, splitting the OTU-N into N optical sub-channel transport units (OTUsubs), wherein a rate of each OTUsub equals the reference rate; and sending the N OTUsubs to an optical interface.
 2. The method according to claim 1, wherein one of the N OTUsubs includes OTU-N overhead and optical channel data unit-N(ODU-N) overhead.
 3. The method according to claim 1, wherein a frame structure of the OTU-N is formed of N subframes, and a rate of each subframe equals the reference rate.
 4. The method according to claim 1, further comprising: adding forward error correction (FEC) overhead information to each OTUsub.
 5. A transmission apparatus for use in an optical transport network, the transmission apparatus comprising: a computing hardware; and a non-transitory computer-readable storage medium including computer-executable instructions, when executed by the computing hardware, cause the transmission apparatus to: map a client signal into an payload area of an optical channel transport unit-N (OTU-N), wherein a rate of the OTU-N is N times a reference rate, and the value N is a positive integer, split the OTU-N into N optical sub-channel transport units (OTUsubs), wherein a rate of each OTUsub equals the reference rate, and send the N OTUsubs to an optical interface.
 6. The transmission apparatus according to claim 5, wherein one of the N OTUsubs includes OTU-N overhead and optical channel data unit (ODU-N) overhead.
 7. The transmission apparatus according to claim 5, wherein a frame structure of the OTU-N is formed of N subframes, and a rate of each subframe equals the reference rate.
 8. The transmission apparatus according to claim 5, wherein the computer-executable instructions, when executed by the computing hardware, further cause the transmission apparatus to: add forward error correction (FEC) overhead information to each OTUsub.
 9. A receiving apparatus in an optical transport network, the receiving apparatus comprising: a computing hardware; and a non-transitory computer-readable storage medium including computer-executable instructions which, when executed by the computing hardware, cause the receiving apparatus to: receive N optical sub-channel transport units (OTUsubs), wherein a rate of each OTUsub equals a reference rate; multiplex the N OTUsubs into one optical channel transport unit-N(OTU-N), wherein a rate of the OTU-N is N times the reference rate, and the value N is a positive integer; and demap a client signal from a payload area of the OTU-N.
 10. The receiving apparatus according to claim 9, wherein the computer-executable instructions, when executed by the computing hardware, further cause the receiving apparatus to: align the N OTUsubs, and multiplex the aligned N OTUsubs into one OTU-N.
 11. The receiving apparatus according to claim 9, wherein one of the N OTUsubs includes OTU-N overhead and optical channel data unit (ODU-N) overhead.
 12. The receiving apparatus according to claim 9, wherein a frame structure of the OTU-N is formed of N subframes, and a rate of each subframe equals the reference rate.
 13. The receiving apparatus according to claim 9, wherein the computer-executable instructions, when executed by the computing hardware, further cause the receiving apparatus to: perform forward error correction (FEC) decoding for the aligned N OTUsubs, and multiplex the N OTUsubs into one OTU-N.
 14. The receiving apparatus according to claim 9, wherein the computer-executable instructions, when executed by the computing hardware, further cause the receiving apparatus to: receive one or more optical carriers from a same fiber; and demodulate N OTUsubs out of the one or more optical carriers. 